Formation of helical
multishell gold nanowire
Theory :Y. Iguchi, T. Hoshi and T. Fujiwara, PRL 99, 125507 (2007)
T. Hoshi and T. Fujiwara, JPCM21, 272201 (2009).
T. Hoshi, Y. Iguchi, and T. Fujiwara, Handbook of NanoPhysics 4,
Ed. D. Sattler, CRC Press, pp.36.1-18, (2010)(*)
ex. ‘11-4’-type nanowire
with L = 12 nm
section view (11-4 structure) Experiment :
Y. Kondo and K. Takayanagi, Science 289, 606 (2000)
(*) Preprint:
Formation of helical
multishell gold nanowire
Theory :Y. Iguchi, T. Hoshi and T. Fujiwara, PRL 99, 125507 (2007)
T. Hoshi and T. Fujiwara, JPCM21, 272201 (2009).
T. Hoshi, Y. Iguchi, and T. Fujiwara, Handbook of NanoPhysics 4,
Ed. D. Sattler, CRC Press, pp.36.1-18, (2010)(*)
ex. ‘11-4’-type nanowire
with L = 12 nm
section view (11-4 structure) Experiment :
Y. Kondo and K. Takayanagi, Science 289, 606 (2000)
(*) Preprint:
http://www.damp.tottori-u.ac.jp/~hoshi/info/2010_Hoshi_AuNW_HNP_preprint.pdf
: 7-1, 11-4, 13-6, 14-7-1, 15-8-1 structures Specific shell configurations
with "magic number"
Geometrical theory for helical multishell gold nanowires
Initial non-helical structure in ideal FCC geometries
“Magic number” for specific multishell configuration
(1) no acute angle on the surface
(2) no (001)-like (square) side longer than any (111)-like (hexagonal) side
Rule for initial structural model
Add one atom row
10- 4
11- 4
6- 1
7- 1
[110] (001) (110) RelaxationTwo-stage formation model for helical structure
(1) Dissociation of the outermost shell from the inner shells (2) Slip deformation at the outermost shell
: from (001)-like (square) str. into (111)-like (hexagonal) str.
ex. 11-4 structure
B
(1)
(2)
Two-stage formation model for helical multishell gold nanowires
in various (experimentally observed) multishell configurations
(a) 7-1 (section view)
(b) 11-4
(c) 12-6-1
(d) 13-6-1
(e) 14-7-1
(f) 15-8-1
simulation steps
13-5-1
( 13-6 ?)
non-helical helical
Two-stage formation model for helical multishell gold nanowires
( Physical origin: wide 5d band )
non-helical
helical
Fig. expanded lateral surface (schematic)
(1) Dissociation of the surface (outermost) shell from the inner shells (2) Shear-like deformation at the surface shell
non-helical helical
Two-stage formation model for helical multishell gold nanowires
( Physical origin: wide 5d band )
non-helical
helical
Fig. expanded lateral surface (schematic)
What occurs
at domain bounary ?
[ Our short answer :
An atom pair is inserted ]
(1) Dissociation of the surface (outermost) shell from the inner shells (2) Shear-like deformation at the surface shell
Defect-induced helicity
by atom movement from inner shell
(11-4) type, (length) = 12 nm
Multiple helical domains
with different twisting directions A posible thinning process (?)
Relaxation simulation with longer nanowire (L=12 nm)
‘Green’ atom pairs are moved from the inner shell --> Helical domain boundary
Shear-like deformation on ‘red’ atoms : square --> hexagonal
oppsite shear directions
between left and right domains A B C C A D F D E
Relaxation simulation with longer nanowire (L=12 nm)
Initial
Final
‘Green’ atom pairs are moved from the inner shell --> Helical domain boundary
Red atoms: initially on the (001)-type
(square-lattice) surface area Green atoms: initially in the inner shell
Technical details ( Iguchi, Hoshi, Fujiwara, PRL99, 125507 (2007) )
Relaxation with thermal motion ( T = 600K, dt = 1fs ) Tight-binding Hamiltonian in the NRL form
Kirchhoff,et al. PRB63, 195101 (2001) da Silva et al. PRL 87, 256102 (2001).
Amorim and da Silva PRL 101, 125502 (2008)
Total energy [au]
Analysis : Why gold forms helical nanowire ?
‘Nanoscale competition’ beween
(a) Energy gain of helical transfomation on surface (’red’ atoms) (b) Energy loss of at domain boundary ( ’green’ atoms )
→ surface stabilization mechanism
→ simple energy scaling theory with domain length L
(a) ∆E
~O(L)
(b) ∆E~O(1)
Energy [eV] Energy [eV]
final LDOS [ states/eV ] (a) (b) initial final initial
Physical origin : wide 5d band of gold (unlike 3d, 4d metals)
consistent to the features in reconstruction on equllibrium surfaces →
Change of the atom energy during the relaxation simulaiton
Iteration step Iteration step
Atom energy [eV]
P, Q : Atoms with energy gain (in surface reconstruction)
A simple energy-scaling theory with respect to domain length
Competitive feature of
(a) Energy gain of surface reconstruction (’red’ atoms) ( shear-like deformation : square --> hexagonal )
(b) Energy loss of defect fomation at domain boundary ( ’green’ atoms ) ( atom movement into wire surface)
= - 1.2 eV per unit layer
= + 2.4 eV at domain bounary
> 2 unit layers
Conclusion: Helical domain formation on multishell gold nanowire
Surface stabilization mechanism with > 2 unit layers (a) Energy gain of surface reconstruction
( shear-like deformation : square --> hexagonal ) (b) Energy loss of defect fomation at domain boundary ( atom pair supply into wire surface)
The same explanation holds on the equillibrium surfaces :
Reconstruction into (111)-like (hexagonal) strucutre on the Au(110) surface Possible physical origin : wide 5d band
DOS of FCC Cu, Ag, Au
‘Missing row’ structure in FCC(110) surface
→ (111)-type surface regions as successive nanofacets top
view
side view
Experiment: thinning process
of gold multishell nanowire
Y. Oshima, Y. Kondo, K. Takayanagi, J. Elec. Microsc. 52, 49-55 (2003)
in situ TEM images